It's Tom Miller Big Wheel, from The Unicycle Factory. It's serial # 30, from 1982. Built like a Schwinn, with same style of frame, bearings and Schwinn seat. The seat has a sheepskin cover on it that was actually made for Schwinn unicycle seats! A protoype, probably. The hard rubber tire makes it great for spins, bad for long rides. Weight is about 28-29 pounds. See more pictures of it here.